Electron emitting element and image forming apparatus employing it

ABSTRACT

An electron emitting element is of a structure in which a semiconductor layer is formed between an upper electrode and a lower electrode, wherein an organic compound adsorption layer is formed on a semiconductor surface of the semiconductor layer by causing the organic compound to be adsorbed on the semiconductor surface. Herein, the semiconductor layer can be made of silicon or polysilicon and partly or as a whole porous. The absorbed organic compound can be a non-cyclic hydrocarbon, a compound obtained by coupling at least an aldehyde group to a non-cyclic hydrocarbon, or a non-cyclic hydrocarbon having an unsaturated bond. As a result, there can be provided an electron emitting element capable of stably operating in the atmosphere or in a low vacuum even when being operated in the atmosphere or in the low vacuum and an imaging device using the electron emitting element.

TECHNICAL FIELD

The present invention relates to an electron emitting element capable ofstably operating for a long period of time even in the atmosphere, andan imaging device using the same.

BACKGROUND ART

A Spindt-type electrode, a carbon nanotube (CNT)-type electrode and thelike have been known as conventional cold cathode-type electron emittingelements, which have been studied on applications to the field of FED(Field Emission Display). The elements are operated in such a mannerthat a voltage is applied to a pointed end to form a strong electricfield of about 1 GV/m and to emit electrons with the help of a tunnelingeffect.

There has been heretofore present an idea that such an electron emittingelement is operated in the atmosphere and applied to a charger or anelectrostatic latent image forming device. For example, there has beenproposed a method in which a Spindt-type cold cathode is operated in theatmosphere to emit electrons into the atmosphere, to ionize gasmolecules into ions as charged particles and to form an electrostaticlatent image (see Japanese Laid-Open Patent Publication No. 06-255168).Besides, the result of a research on a carbon nanotube operated in theatmosphere has been reported (see Yamaguchi and three others,“Development of High Efficiency Electron Source for Image Recording withCarbon Nanotube,” Japan Hardcopy 97 articles, The Imaging Society ofJapan, July 1997, pp 221-224). As seen from the documents, suggestionhas been given on a possibility of applying an electron emission elementas an electron source for an electrophotograph charger or electrostaticlatent image forming device.

The two types of electron emitting elements, however, have a strongelectric field in the vicinity of a surface of an electron emittingsection as described above, which makes it easy that emitted electronsacquire energy larger than the electric field to ionize gas molecules.This has resulted in a problem that plus ions generated by ionization ofgas molecules are accelerated by the strong electric field in thedirection toward the element surface and collide with the elementsurface, causing element breakdown due to sputtering.

There have been known other type cold cathodes such as an MIM (MetalInsulator Metal) type and an MIS (Metal Insulator Semiconductor) type.Those are a surface emission-type electron emitting element working in away such that electrons are accelerated using a quantum size effect anda strong electric field and caused to be emitted from a flat elementsurface. The electron emitting elements have no necessity for a strongelectric field outside of the element since electrons are acceleratedinside of the element and emitted. Hence, an electron emitting elementof the MIM type or the MIS type can solve a problem that the element isbroken down by sputtering through ionization of gas molecules, whichoccurs in the electron emitting element of the Spindt type or the CNTtype.

An electron emitting element in which electrons injected into a poroussemiconductor are accelerated in an electric field, forced to passthrough a surface metal thin film with the help of a tunneling effectand finally emitted into a vacuum has been proposed as an electronemitting element belonging to the MIS type using a quantum size effectof a porous semiconductor (for example, porous silicon) formed by ananodic oxidation treatment on a semiconductor (see Japanese Laid-OpenPatent Publication No. 08-250766). A cold cathode made of such a poroussemiconductor has a great merit that an element can be fabricated bymeans of an extremely simple, convenient, low-cost method adoptinganodic oxidation.

In a case where such an element is operated in the atmosphere, however,a problem has newly occurred that various gas molecules are adsorbed ona surface of the element to change an electric characteristic or thelike of the semiconductor and to thereby reduce an electron emissioncurrent.

The surface of a cold cathode of the MIM type or the MIS type insidewhich element electrons are accelerated is constituted generally of ametal thin film playing a role as an upper electrode applying anelectric field to the inside of the element. Since electrons acceleratedin the inside of the element, however, are emitted into a vacuumtunneling through the surface metal thin film, an tunneling effectenhanced with a smaller film thickness increases an electron emissionquantity. A thickness of the metal film by which the two roles areestablished simultaneously has been appropriate in the range of fromseveral nm to tens of nm. For example, in Japanese Laid-Open PatentPublication No. 08-250766, there is disclosed an example with athickness of a metal thin film of 15 nm.

Cold cathodes of the MIM type and the MIS type have difficulty forming adense metal film because of a very thin film on the surfaces thereof andalmost no barrier effect to gas molecules is exerted. Therefore, in acase where an electron emitting element is operated in the atmosphere, aproblem arises that gas molecules intrude into an inside semiconductorlayer to change an electric characteristic or the like of thesemiconductor to thereby reduce an electron emission current.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an electron emittingelement capable of stably operating in the atmosphere or in a low vacuumby solving the above problems when being operated in the atmosphere orin the low vacuum, and to provide an imaging device using the electronemitting element.

The electron emitting element according to the present invention, inorder to achieve the object, is directed to an electron emitting elementof a structure in which a semiconductor layer is formed between an upperelectrode and lower electrode, wherein an organic compound adsorptionlayer is formed on a semiconductor surface of the semiconductor layer bycausing the organic compound to be adsorbed on the semiconductorsurface. The semiconductor layer here is made of silicon or polysiliconand part or the whole thereof can be made porous. The organic compoundcan be a straight-chain or branched non-cyclic hydrocarbon having 7 ormore carbon atoms in a molecule, a compound obtained by coupling atleast an aldehyde group to a non-cyclic hydrocarbon, or a non-cyclichydrocarbon having at least one unsaturated bond in a molecule.

The imaging device according to the present invention is directed to animaging device using the electron emitting element according to thepresent invention as a charger, wherein an electrostatic latent imagecarrier is charged by emitting electrons from the electron emittingelement in the atmosphere. The imaging device according to the presentinvention is directed to an imaging device using the electron emittingelement according to the present invention as a charge feed device,wherein a latent image is formed directly on an electrostatic latentimage carrier by emitting electrons from the electron emitting elementin the atmosphere.

According to the present invention, as described above, an electronemitting element in which a semiconductor layer is formed between anupper electrode and lower electrode is constructed and an organiccompound is caused to be adsorbed on a semiconductor surface of thesemiconductor layer, thereby enabling an electron emitting elementcapable of stably operating even in the atmosphere to be provided andfurther an imaging device using the electron emitting element to beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an electron emitting elementaccording to the present invention.

FIG. 2 is a schematic view showing another electron emitting elementaccording to the present invention.

FIG. 3 is a view illustrating a driving method for an electron emittingelement according to the present invention.

FIG. 4 is a graph showing a current-voltage characteristic of such anelectron emitting element according to the present invention.

FIG. 5 is a graph showing degradation in characteristic while aconventional electron emitting element is continuously driven.

FIG. 6 is a graph showing degradation in characteristic while anelectron emitting element according to the present invention and aconventional electron emitting element are continuously driven.

FIG. 7 is a graph showing degradation in characteristic while anotherelectron emitting element according to the present invention and aconventional electron emitting element are continuously driven.

FIG. 8 is a representation illustrating adsorption on a semiconductorsurface of an organic compound in the present invention.

FIG. 9 is a representation illustrating adsorption on a semiconductorsurface of another organic compound in the present invention.

FIG. 10 is a schematic view showing a charger using an electron emittingelement according to the present invention.

FIG. 11 is a schematic view showing an imaging device using an electronemitting element according to the present invention as a charger.

FIG. 12 is a schematic view showing an imaging device using an electronemitting element according to the present invention as a charge feeddevice.

FIG. 13 is a schematic view showing a charge feed device using anelectron emitting element according to the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 or 2, an electron emitting element according tothe present invention is an electron emitting element 11 or 12 of astructure in which a semiconductor layer 14 or 24 is formed between anupper electrode 16 or 26 and a lower electrode 13 or 23, characterizedby that an organic compound is caused to be adsorbed on a semiconductorsurface of the semiconductor layer to thereby form an organic compoundadsorption layer 15 or 25. By causing an organic compound to be adsorbedon the semiconductor surface, the semiconductor surface is stabilized,gas molecules in the atmosphere is prevented from being adsorbed on thesemiconductor surface and a change in electric characteristic caused bythe gas molecules and reduction in electron emission current of theelectron emitting element can be suppressed. No specific limitation isplaced on a thickness of the organic compound adsorption layer as far asit does not affect adversely the object of the present invention, andthe thickness is preferably as thin as possible on the order of amonomolecular layer from the viewpoint of an electron emissioncharacteristic of the electron emitting element. An organic compound isadsorbed at a portion having adsorption activity on a semiconductorsurface (for example, a hydrogen terminal on a polysilicon semiconductorsurface) to form an organic compound adsorption layer and to therebyenable the semiconductor surface to be stabilized; therefore, in thepresent invention, the organic compound adsorption layer has only to beformed on at least portions with adsorption activity on thesemiconductor surface and is not required to completely cover the entiresemiconductor surface.

The semiconductor layer of the electron emitting element according tothe present invention can be a porous silicon semiconductor layer or aporous polysilicon semiconductor layer in which part or all of siliconor polysilicon is made porous. A porous silicon semiconductor layerobtains a large emission current, while a porous polysiliconsemiconductor layer greatly improves thermal stability. A poroussemiconductor layer is high in effect of semiconductor surfacestabilization with adsorption of an organic compound. Herein, the term,polysilicon, means polycrystalline silicon.

In a case where a semiconductor layer is porous, a semiconductor surfaceincludes not only a surface of the semiconductor layer, but also asemiconductor surface in the inside of the semiconductor layer on whichan organic compound can be adsorbed by way of holes formed inside thesemiconductor layer. That is, in a case where semiconductor is porous,an organic compound is adsorbed on the semiconductor layer and thereby,not only is organic compound adsorption layer 15 or 25 formed on asurface of semiconductor layer 14 or 24 shown in FIG. 1 or 2, but anorganic compound adsorption layer (not shown) is also formed on thesemiconductor surface in the inside of the semiconductor layer.

An electron emitting element of the present invention can use anon-cyclic hydrocarbon as the organic compound. A non-cyclic hydrocarboncan be adsorbed on a semiconductor surface of a semiconductor layer tothereby cause hydrophobicity to exerted. Thereby water molecules in theatmosphere can be prevented from intruding into the semiconductor layerand an oxidation reaction of a semiconductor layer with water moleculescan also be prevented from occurring, which makes it possible tosuppress a change in electric characteristic and reduction in electronemission current of an electron emission element. Since a non-cyclichydrocarbon is less in steric hindrance as compared with a cyclichydrocarbon, the non-cyclic hydrocarbon can be adsorbed on asemiconductor surface at a higher density, thereby hydrophobicity of thesemiconductor surface can be raised.

An electron emitting element according to the present invention can usea straight-chain or branched non-cyclic hydrocarbon having 7 or morecarbon atoms as the non-cyclic hydrocarbon. Such a non-cyclichydrocarbon is attached to a semiconductor surface and becomes asaturated hydrocarbon to thereby form a chemically stable semiconductorsurface extremely low in reactivity with an oxidant, a reductant, anacid or a base. The term, a branched non-cyclic hydrocarbon, means anon-cyclic hydrocarbon having at least one branching.

An electron emitting element according to the present invention can usea compound obtained by coupling at least an aldehyde group to thenon-cyclic hydrocarbon as the organic compound. In a case of anon-cyclic hydrocarbon, or especially in a case where a non-cyclichydrocarbon is a saturated hydrocarbon, the hydrocarbon is poor inreactivity with a surface of semiconductor such as silicon to renderchemical adsorption thereof difficult. In such a case, when a compoundwith an alkyl group coupled with an aldehyde group as a functional groupis forced to act on a semiconductor surface such as silicon surface, analdehyde group with a high reactivity reacts and is adsorbed on thesemiconductor surface to enable a structure in which the semiconductorsurface is surrounded with alkyl groups to be realized. If a non-cycliccompound having carbon atoms in number exceeding 17 is used, aproportion of aldehyde groups contained in the compound decreases, whichin turn, reduces chemical adsorptivity to a semiconductor layer surface.

Examples of compounds obtained by coupling an aldehyde group to theabove-mentioned non-cyclic hydrocarbon includes: n-octanal(CH₃(CH₂)₆CHO), n-decanal (CH₃(CH₂)₈CHO), n-dodecanal (CH₃(CH₂)₁₀CHO),6-methylpeptanal ((CH₃)₂CH(CH₂)₄CHO), 11-methyldodecanal((CH₃)₂CH(CH₂)₁₀CHO) and others.

An electron emitting element according to the present invention can usea non-cyclic hydrocarbon having at least one unsaturated bond as thenon-cyclic hydrocarbon. Especially, in a case where a non-cyclichydrocarbon is a saturated hydrocarbon, the hydrocarbon is poor inreactivity with a surface of semiconductor such as silicon, resulting indifficulty of chemical adsorption. In such a case, when a non-cyclichydrocarbon having at least one unsaturated bond such as a double bondor a triple bond having a high reactivity is forced to act on a surfaceof semiconductor such as silicon, portions of double bonds or triplebonds having a high reactivity react with and are adsorbed on thesemiconductor surface to enable a structure in which the semiconductorsurface is surrounded with alkyl groups to be realized. If a non-cyclichydrocarbon, with an unsaturated bond, and having carbon atoms in numberexceeding 17 is used, a proportion of unsaturated bonds contained in thenon-cyclic hydrocarbon decreases, leading to reduction in chemicalabsorptivity to a semiconductor surface.

Examples of non-cyclic hydrocarbons having the unsaturated bond include:1-octene (CH₃(CH₂)₅CH═CH₂), 1-decene (CH₃(CH₂)₇CH═CH₂), 1-dodecene(CH₃(CH₂)₉CH═CH₂), 1-hexadecene (CH₃(CH₂)₁₃CH═CH₂), 6-methyl-1-heptene((CH₃)₂CH(CH₂)₄CH═CH₂), 2-methyl-1-nonene (CH₃(CH₂)₆C(CH₃)═CH₂),11-methyl-1-tridecene ((CH₃)₂CH(CH₂)₈CH═CH₂), 2,4-dimethyl-1-heptene(CH₃(CH₃)₂CH (CH₃)CH₂C(CH₃)═CH₂), 1,7-octadiene (CH₂═CH(CH₂)₄CH═CH₂),1,3-decadiene (CH₃(CH₂)₅CH═CH—CH═CH₂) and others.

An electron emitting element according to the present invention can usea straight chain or branched non-cyclic unsaturated aldehyde compoundexpressed in a formula of C₂H_(2n−1)CHO (n is an integer ranging from 7to 17) as a compound obtained by coupling an aldehyde group to theabove-mentioned non-cyclic hydrocarbon. With the presence of an aldehydegroup and an unsaturated bond in a molecule, a reactivity with asemiconductor surface further increases, thereby enabling a strongerchemical adsorption to be realized. Examples of such compounds include:2-octenal (CH₃(CH₂)₄CH═CHCHO), 2-decenal (CH₃(CH₂)₆CH═CHCHO),2-dodecenal (CH₃(CH₂)₈CH═CHCHO), 2-hexadecenal (CH₃(CH₂)₁₂CH═CHCHO),6-methyl-2-heptenal (CH₃)₂CH(CH₂)₂CH═CHCHO), 11-methyl-2-dodecenal((CH₃)₂CH(CH₂)₇CH═CHCHO), 2,6-dimethyl-5-heptenal ((CH₃)₂C═CH(CH₂)₂CH(CH₃)CHO) and others.

The imaging device according to the present invention is directed to animaging device using the electron emitting element according to thepresent invention as a charger, wherein the electron emitting elementemits electrons into the atmosphere to charge an electrostatic latentimage carrier. The electron emitting element according to the presentinvention can stabilize a semiconductor surface of a semiconductor layerby causing an organic compound to be adsorbed on the semiconductorsurface to prevent gas molecules in the atmosphere from being adsorbedon the semiconductor surface and to thereby enable a change in electriccharacteristic and reduction in an electron emission current in theelectron emitting element caused by the gas molecules to be suppressed;therefore, the element is used as a charger to thereby enable anelectrostatic latent image carrier to be charged.

The imaging device according to the present invention is directed to animaging device using the electron emitting element according to thepresent invention as a charge feed device, wherein the electron emittingelement is caused to emit electrons in the atmosphere to form a latentimage directly on the electrostatic latent image carrier. The electronemitting element according to the present invention can stabilize asemiconductor surface of a semiconductor layer by causing an organiccompound to be adsorbed on the semiconductor surface to prevent gasmolecules in the atmosphere from being adsorbed on the semiconductorsurface and to thereby enable a change in electric characteristic andreduction in an electron emission current in the electron emittingelement caused by the gas molecules to be suppressed; therefore, theelement is used as a charge feed device to thereby enable a latent imageto be formed directly on an electrostatic latent image carrier.

Therefore, the imaging device according to the present invention isconstructed as a more simplified imaging device without generatingozone, which has been problematic in a conventional discharge-typecharger.

Description will be given of embodiments of the present invention in aconcrete manner below based on the accompanying drawing.

EMBODIMENT 1

With reference to FIG. 1, an electron emitting element 11 according tothe present invention has a structure in which a porous polysiliconlayer as a semiconductor layer 14 is formed on a semiconductor substrate13 b made of n-type silicon on the rear surface of which an ohmicelectrode 13 a is formed, an organic compound is caused to be adsorbedon a polysilicon surface of the porous polysilicon layer to form anorganic compound adsorption layer 15, and an upper electrode 16 isformed on a surface thereof. Not only is organic compound adsorptionlayer 15 shown in FIG. 1 formed on a surface of the porous polysiliconlayer, but an organic compound adsorption layer is formed on apolysilicon surface in the inside of the porous polysilicon layer,though not shown. Semiconductor substrate 13 b made of n-type siliconhas a high electric conductivity and has a function as a lower electrode13 integrally in a piece with ohmic electrode 13 a.

The porous polysilicon layer was prepared by means of the followingmethod. First of all, an undoped polysilicon layer with a thickness ofabout 1.5 μm was formed on a surface of conductive substrate 13 b madeof n-type silicon by means of a LPCVD (Low Pressure Chemical Vapordeposition) method. Then, a constant current anodic oxidation treatmentwas applied to the polysilicon layer in a mixed solution of a 50 mass %hydrofluoric acid aqueous solution and ethanol with a mixing ratio of 1to 1 with the polysilicon layer as a positive electrode and a platinumelectrode as a negative electrode to thereby render part or the whole ofthe polysilicon layer porous and to obtain the porous polysilicon layer.Pore diameters of the porous polysilicon layer were on the order in therange of about 10 nm to 100 nm. Note that a surface of the polysiliconlayer is illuminated with light during anodic oxidation treatment usinga tungsten lamp of 500 W. At the last stage, the porous polysiliconlayer was applied with an RTO (Rapid Thermal Oxidation) treatment atabout 900° C. to form an oxide film.

Then, an organic compound was caused to be adsorbed on the polysiliconsurface of the porous polysilicon layer obtained as described above tothereby form organic compound adsorption layer 15. For example, theelement with the porous polysilicon layer was sufficiently dehydratedand thereafter, the element was put into n-decanal (CH₃(CH₂)₈CHO) keptat 90° C. The element was kept in n-decanal for about 30 minutes,thereby, as shown in FIG. 8, a reaction occurs between hydrogenterminals remained on the polysilicon surface of the porous polysiliconlayer and an aldehyde group of n-decanal and a long chain alkyl group(n=9) of n-decanal is chemically adsorbed on the polysilicon surface toform an organic compound adsorption layer.

In addition, as shown in FIG. 1, a gold electrode thin layer as upperelectrode 16 was formed on a surface of organic compound adsorptionlayer 15 formed to a thickness of about 15 nm on the polysilicon surfaceof the porous polysilicon layer, which is semiconductor layer 14, bymeans of a vapor deposition method or a sputtering method to therebyobtain electron emitting element 11 according to the present invention.Note that materials of the electrode thin film layer that can be usedinclude: metals such as gold; in addition thereto, aluminum, tungsten,nickel, platinum, chromium and titanium, and metal oxides such as ITO(Indium Tin Oxide).

The electron emitting element fabricated as described above can bedriven in a way as described below. That is, with reference to FIG. 3, acollector electrode 37 is arranged at a position opposite upperelectrode 16 of electron emitting element 11 with a spacing therebetweenof 1 mm, a direct current voltage Vps is applied between upper electrode16 (positive electrode) and lower electrode 13 (negative electrode), anda direct current voltage Vc of 100 V is further applied betweencollector electrode 37 and upper electrode 16 to thereby drive theelectron emitting element so as to emit electrons 30.

Measurement was carried out on a diode current Ips flowing between upperelectrode 16 and lower electrode 13 and an emission current le flowinginto collector electrode 37 by electrons emitted from upper electrode 16and minus ions in the atmosphere and results are shown in FIG. 4. InFIG. 4, the abscissa shows a value of direct voltage Vps applied to theelectron emitting element and the ordinate shows a current density on alogarithmic scale, where the rhombus mark indicates diode current Ipsand the square mark shows emitted electron current Ie.

As shown in FIG. 4, when element applied voltage Vps was set to 21 V, anemission current Ie of 4.5 μA/cm² was observed despite of operation inthe atmosphere. Most of the current is thought to be a currenttransported to the collector electrode in a state where electronsemitted from the electron emitting element according to the presentinvention are attached to gas molecules to form minus ions. A currentquantity of 4.5 μA/cm² is a current quantity applicable to charging aphotosensitive member in an electrophotographic technology used in alaser printer or a digital copying machine and the charge of aphotosensitive member can realized in a construction in which collectorelectrode 37 is replaced with the photosensitive member (not shown) inFIG. 3.

For the sake of reference, FIG. 5 shows results of measurement on achange in electron emission current quantity while a conventionalelectron emitting element on which no organic compound was adsorbed on asurface of the semiconductor layer was continuously driven. While anelectron emitting element fabricated by means of a method in which anoxide film is formed by RTO after the polysilicon layer is renderedporous by anodic oxidation as described above was continuously driven inthe atmosphere and argon (Ar) at the atmospheric pressure, degradationin characteristic was measured, and the results are shown with a fineline and a heavy line, respectively, in FIG. 5. Degradation in argon atthe atmospheric pressure is small, whereas current degradation is asgreat as almost three or more orders of magnitude in the atmosphere thanin argon. It is found from the experimental results in Ar that theelectron emitting element of the present invention is stably operatedwithout receiving sputtering breakdown caused by ionization of gasmolecule even if being operated at the atmosphere. It was found from theexperiments in the atmosphere that the element is greatly degraded by anfactor or factors other than the sputtering breakdown by ions. That is,it is imagined that in the atmosphere, since various kinds of gasmolecules (such as nitrogen, oxygen, carbon dioxide, water, methane,hydrogen, nitrogen oxides and ammonia) that constitute air are adsorbedon a semiconductor surface of a semiconductor layer of an electronemitting element, chemical reaction occurs between the gas molecules anda polysilicon surface of a polysilicon layer, which is a semiconductorlayer, especially while the electron emitting element is driven tochange a quality of the electron emitting element so as to degrade acharacteristic.

A thickness of a metal thin film of upper electrode of an electronemitting element is about 15 nm. An upper electrode of such a thin filmis difficult forming a dense thin film without no clearance, whichenables various gas molecules in the atmosphere to pass through theupper electrode. Besides, even if a polysilicon layer of an electronemitting element is rendered porous by anodic oxidation and an oxidefilm is formed thereon by RTO or the like to cover a surface of thepolysilicon layer with a thin film of SiO₂, the SiO₂ film is not densebecause of being a thin film and a polysilicon surface having hydrogenterminals remains. Hence, it is imagined that molecules of oxygen,nitrogen and water present in the atmosphere are adsorbed at thehydrogen terminals on the polysilicon layer surface and then, a chemicalreaction such as oxidation occurs under influence of a current generatedby driving the element, which degrades element characteristic.

FIG. 6 shows a change in electron emission current quantity as a heavyline while an electron emitting element (an inventive element in theexample shown in FIG. 6) according to the present invention having asemiconductor surface of a semiconductor layer on which an organiccompound is adsorbed was continuously driven. Note that a fine line ofFIG. 6 shows a change in an electron emission current quantity of aconventional electron emitting element (a conventional element in thecomparative example shown in FIG. 6) having a semiconductor surface of asemiconductor layer on which no organic compound is adsorbed wascontinuously driven. As shown in FIG. 6, by adsorbing n-decanal on asemiconductor surface of the semiconductor layer, an electron emissioncurrent quantity after 5 minutes was improved by a 0.37 digit inmagnitude and an electron emission quantity after 30 minutes wasimproved by a 0.82 digit of magnitude.

It is imagined that since an organic compound is adsorbed on thesemiconductor surface of a semiconductor layer to thereby form anorganic compound adsorption layer obtained by replacing hydrogenterminals of polysilicon present on the semiconductor surface with alkylgroups, an electron emission characteristic of the electron emittingelement can be stabilized. That is, it is imagined that by causing longchain alkyl groups to be adsorbed on the semiconductor surface of asemiconductor layer, the semiconductor surface of a semiconductor layercan be protected from adsorption of various gas molecules in theatmosphere and the quasi-active semiconductor surface easy to react withgas molecules (hydrogen terminals or the like on the polysiliconsemiconductor surface) can be subjected to chemical adsorption with anorganic compound and stabilized; therefore, degradation while continuousdriving can be overcome. Besides, it is inferred that since long chainalkyl groups exert hydrophobicity, the alkyl groups prevent adsorptionof water and excessive progress in oxidation, thereby stabilizing theelement.

As described above, by causing an organic compound to be absorbed on asemiconductor surface of a semiconductor layer to form an organiccompound adsorption layer, an electron emitting element operating stablyfor a long time in the atmosphere can be realized.

EMBODIMENT 2

Another electron emitting element according to the present invention (aninventive element in the example shown in FIG. 7) was fabricated in asimilar way to that in Embodiment 1 with the exception that n-dodecanal(CH₃(CH₂)₁₀CHO) was used when an organic compound is adsorbed on apolysilicon surface of a porous polysilicon layer. FIG. 7 shows a changein electron emission current quantity with a heavy line while theinventive element was continuously driven in a similar way to that inEmbodiment 1. A fine line in FIG. 7 shows a change in electron emissionquantity of a conventional electron emitting element having asemiconductor surface of a semiconductor layer on which no organiccompound is adsorbed (a conventional element in the comparative exampleof FIG. 7) with a fine line while the conventional element was operatedcontinuously in the same way. As shown in FIG. 7, by causing n-dodecanalto be absorbed on a surface of a semiconductor layer, an electronemission current quantity after 5 minutes is increased by 1.32 digits inmagnitude.

EMBODIMENT 3

Electron emitting element 11 according to the present invention wasobtained in a similar way to that in Embodiment 1 with the exceptionthat 1-decene (CH₃(CH₂)₇CH═CH₂) was used when an organic compound wascaused to be adsorbed on a silicon surface of a porous polysiliconlayer. By adsorption of 1-decene to the silicon surface of a porouspolysilicon layer, a reaction occurs, as shown in FIG. 9, betweenhydrogen terminals remaining on the porous polysilicon surface and avinyl group of 1-decene and as a result, a long chain alkyl group (n=9)of 1-decene is chemically adsorbed on the polysilicon surface to therebyform an organic compound adsorption layer.

Note that an adsorption state of an organic compound, that is a state ofan organic compound adsorption layer, on the silicon surface can beanalyzed with DRIFT (Diffuse Reflectance Infrared Fourier-transform),Auger electron spectroscopy, Raman spectroscopy or the like.

EMBODIMENT 4

With reference to FIG. 2, another electron emitting element 21 accordingto the present invention has a structure in which a lower electrode 23is formed on a surface of an insulating substrate 22 made of glass, aporous polysilicon layer is formed as a semiconductor layer 24 thereon,an organic compound is caused to be adsorbed on a polysilicon surface ofthe porous polysilicon layer to form an organic compound adsorptionlayer 25, and an upper electrode 26 is further formed on the surface. Inthis case, not only is organic compound adsorption layer 25 shown inFIG. 2 formed on the surface of the porous polysilicon layer, but anorganic compound layer, though not shown, is also formed on apolysilicon surface in the inside of the porous polysilicon layer.Materials of lower electrode 23 on insulating substrate 22 made of glassthat can be used are, for example, metals such as aluminum, tungsten,gold, nickel, platinum, chromium, titanium and others; metal oxides suchas ITO. Lower electrode 23 is formed by means of a vapor depositionmethod or a sputtering method.

The porous polysilicon layer on the surface of insulating substrate 22on which lower electrode 23 was formed was formed according to a methoddescribed below. An undoped polysilicon layer with a thickness of about1.5 μm was formed on a surface of lower electrode 23 formed on thesurface of insulating substrate 22 made of glass by means of an LPCVDmethod. Then, a constant current anodic oxidation treatment was appliedon the polysilicon layer in a mixed solution of a 50 mass % hydrogenfluoride aqueous solution and ethanol with a mixing ratio of 1 to 1 withthe polysilicon layer as a positive electrode and a platinum electrodeas a negative electrode to thereby render part or the whole of thepolysilicon layer porous to obtain the porous polysilicon layer. Porediameters in the porous polysilicon layer were on the order in the rangeof from about 10 nm to 100 nm. Note that a surface of the silicon layerwas illuminated with light from a tungsten lamp with the output of 500 Wduring anodic oxidation. Finally, a constant current was fed in an about10% dilute sulfuric acid with the silicon substrate as a positiveelectrode and a platinum electrode as a negative electrode to therebyapply an ECO (Electrochemical Oxidation) treatment to the siliconsubstrate and to form an oxide film. In a fabrication process with suchan ECO treatment, a process temperature is low, which alleviates arestraint on a substrate material, thereby enabling glass as a substratematerial to be used. Besides, since, directly subsequent thereto, theporous polysilicon layer can be oxidized with a wet treatment, theprocess can be simplified as compared with oxidation in rapid thermaloxidation.

In a similar way to that in Embodiment 1, an organic compound adsorptionlayer was formed on the polysilicon surface of the porous polysiliconlayer and thereafter, the upper electrode was formed thereon.

EMBODIMENT 5

With reference to FIG. 10, a charger 52 using an electron emittingelement according to the present invention has a structure in which aphotosensitive member 47 constituted of an electrode 48 and aphotosensitive layer 49 is disposed at a position opposite upperelectrode 16 of electron emitting element 11. A spacing between upperelectrode 16 of electron emitting element 111 and photosensitive member47 is set to 1 mm and the photosensitive member was charged inconditions that a collector voltage Vc is set to 800 V and the voltageVps applied to the element is set to 20 V. Since an ion transportelectric field is formed in a space above upper electrode 16 while acharge operation is carried out, emitted electrons 40 are efficientlytransported to the photosensitive member. It is inferred that sinceelectrons are emitted in the atmosphere, a great part of the emittedelectrons are attached to gas molecules in the atmosphere and suchelectrons are transported as minus ions. The electron emitting elementaccording to the present invention with such a construction having thesemiconductor layer on the surface of which an organic compound wasadsorbed was driven and thereby, the surface of the photosensitivemember was able to be charged to a value in the vicinity of 800 V.

EMBODIMENT 6

Detailed description will be given of an imaging device using theelectron emitting element according to the present invention as acharger.

First of all, with reference to FIG. 11, description will be given of anoutline of a construction of the imaging device. A photosensitive member51 is disposed almost in the middle of the imaging device proper andconstitutes a latent image carrier carrying an electrostatic latentimage formed in the shape of a drum rotation-driven at a constant speedin a direction of an arrow mark during an imaging operation. Variouskinds of devices carrying out an imaging process are arranged oppositethe outer surface of photosensitive member 51.

The devices implementing the imaging process include: a charger 52charging the surface of photosensitive member 51 uniformly; an opticalsystem in which the surface of photosensitive member 51 is imagewiseilluminated with exposure light 53 according to an image not shown; adeveloping device 54 for visualizing the electrostatic latent imageformed on the surface of photosensitive member 51 by exposure with theoptical system; a transferring device 55 transferring the developedimage (that is, an image of toner 60) onto a sheet-like paper 61appropriately transported; a cleaning device 56 removing a residualdeveloping agent (residual toner) not transferred onto the surface ofphotosensitive member 51 after the transfer; and a charge removingdevice 57 removing electrostatic charge remaining on the surface ofphotosensitive member 51, which are installed in this order in arotational direction of photosensitive member 51.

Many of Papers 61 are accommodated in, for example, a tray or a cassetteand accommodated papers are fed one piece at a time by a feeding meansto a transfer region, opposite photosensitive member 51 at a positionwhere transferring device 55 is installed, so that the paper coincideswith the leading edge of the toner image formed on the surface ofphotosensitive member 51. Paper 61 after the transfer is separated fromphotosensitive member 51 and further fed to a fixing device 58.

Fixing device 58 fixes an unfixed toner image transferred onto a paperas a permanent image, and includes a heat roller the surface oppositethe toner image of which is heated to a temperature melting and fixingthe toner, and a press roller bringing paper 61 pressed to the heatroller so as to be in close contact with the heat roller side. Paper 61passing through the fixing device 58 is discharged outside the imagingdevice onto a discharge tray not shown through discharging rollers.

The optical system not shown launches an optical image on-off drivenaccording to image data using a semiconductor laser since an imagingdevice of the present invention is a printer or a digital copyingmachine. Especially in a digital copying machine, reflecting light froma manuscript for copying is read by an image reading sensor such as aCCD element is inputted to the optical system including thesemiconductor laser and then, an optical image according to image datais outputted. In a printer, image data from other processing devicessuch as a word processor and a personal computer is converted to anoptical image and paper is illuminated with the optical image. Theconversion to the optical image is carried out using not only asemiconductor laser but also an LED element or a liquid crystal shutter.

In the way described above, if an imaging operation in the imagingdevice gets started, photosensitive member 51 is rotation-driven in thedirection of the arrow mark and the surface of photosensitive member 51is uniformly charged to a potential with a specific polarity by charger52. After the charge, an optical image is launched by exposure light 53in the optical system not shown and an electrostatic latent imageaccording to the optical image is formed on the surface ofphotosensitive member 51. Developing is carried out in next developingdevice 54 to visualize the electrostatic latent image. In one imagingdevice according to the present invention, the developing is one withtoner of one component and the toner is selectively attracted by anelectrostatic force to an electrostatic latent image formed on thesurface of photosensitive member 51 to thereby complete developing.

A toner image thus developed on the surface of photosensitive member 51is electrostatically transferred onto paper 61 transported properly insynchronism with the rotation of photosensitive member 51 withtransferring device 55 disposed in a transfer region. The transfer isperformed by causing the toner image to migrate to the paper 61 sidewhile transferring device 55 charges the rear surface of paper 61 with apolarity opposite a polarity of toner charge. After the transfer, partof the toner image not transferred to the surface of photosensitivemember 51 is left behind thereon, the residual toner is removed from thesurface of photosensitive member 51 with cleaning device 56 and thecharge on the surface of photosensitive member 51 is removed to auniform potential thereon, for example almost zero potential by chargeremoving device 57 for reuse of photosensitive member 51.

On the other hand, paper 61 on which the transfer has been completed isseparated from photosensitive member 51 and paper 61 is transported tofixing device 58. In fixing device 58, the toner image on paper 61 ismelted and press-adhered on paper 61 by a pressure acted thereon betweenthe rollers. Paper 61 having passed through fixing device 58 isdischarged into a discharge tray or the like installed outside theimaging device as the paper on which imaging is completed.

A charger using corona discharge as a working principle has generallyused heretofore as charger 52 of an imaging device of anelectrophotography type. To be concrete, there has been known a wirecharge scheme using tungsten wire with a diameter of the order of 60 μmto which a high voltage is applied; a saw teeth charger scheme applyinga high voltage to a plurality of saw teeth each having a sharply pointedtip; a roller charging scheme applying a high voltage to the roller putinto contact with a photosensitive member and others, whereas since anyof the schemes is a charger using discharge as a principle, it has beenproblematic to generate much of ozone. In a case where electron emittingelement 11 according to the present invention is used as charger 52 ofFIG. 11, discharge is not a principle but electron emission is aprinciple, thereby enabling an imaging device capable of avoidinggeneration of ozone to be provided.

EMBODIMENT 7

Then, detailed description will be given of an imaging device using suchan electron emitting element according to the present invention as acharge feeding device. As described above, it has been common that amethod in which a photosensitive member is uniformly charged, exposurewith a light beam is carried out to thereby form an electrostatic image,while it is also possible that ions are supplied directly onto aninsulating material or a photosensitive member with a charge feed devicesuch as Ion Printing Technology to thereby form an electrostatic latentimage. Such a direct latent image forming scheme can simplifyconventional two processes of charge and exposure into one process,which is advantageous for down sizing of an imaging device. In a casewhere an electrostatic latent image carrier is a photosensitive member,there are a problem of restraint on material and wear and anotherproblem of dielectric break-down in a film; therefore, design items suchas a film thickness and a dielectric item cannot be greatly altered,while in a case where a direct latent image forming scheme with a chargefeed device, a photosensitive member is not necessarily required as anelectrostatic latent image carrier, but a common insulating material canbe used as the carrier. Hence, a freedom in material selection can beenhanced. Thereby, wear resistance and a resolution of an electrostaticlatent image carrier can be improved.

With reference to FIG. 12, description will be given of an outline of animaging process in a case where a charge feed device 72 capable ofdirect latent image formation is used. A difference between the imagingprocess using a conventional photosensitive member shown in FIG. 11 andthe case of FIG. 12 is that an electrostatic latent image carrierchanges from photosensitive member 51 to a dielectric drum 71, and thethree constituents of charger 52, exposure light 53 and a chargeremoving device 57 are replaced with a charge feed device 72. It is onlya difference that an electrostatic latent image forming method changesfrom a combination of a photosensitive member and light to a methodsupplying ions or electrons directly and other processes associatedtherewith are similar. Note that an electrostatic latent image carrieris not necessary required to be a dielectric drum but may be aconventional photosensitive member.

FIG. 13 shows a schematic view showing a structure of charge feed device72. A substrate 81 is constituted of a silicon substrate or a glassplate having a porous polysilicon layer on a polysilicon surface ofwhich an organic compound is adsorbed. A plurality of electron emittingelement sections 83 are arranged on substrate 81. The outermost surfacesof electron emitting element sections 83 are constituted of thin filmupper electrodes and are connected by a driver IC 82 for selectivelydrive-controlling the plurality of elements and wires 84. With thecharge feed device with such a structure adopted, ions or electrons aresupplied directly onto dielectric drum 71 of FIG. 12, thereby enablingan arbitrary electrostatic latent image to be written. Since FIG. 13 isa diagram of an outline of the structure, only 20 electron emittingelement sections are written, while in an actual case, a plurality ofelements are arranged at a density of 600 DPI (Dots per Inch) across alength of about 300 mm to thereby enable an electrostatic latent imagefor a printer or a copying machine capable of handling a paper size aslarge as A3 to be formed.

Since a conventional charge feed device generates ions by discharge as aprinciple in a similar way to that in a conventional charger, a problemhas arisen that generates much of ozone. By using an electron emittingelement of the present invention as charge feed device 72 of FIG. 13,not only can generation of ozone be avoided since discharge is not aprinciple, but electron emission is a principle, but an imaging devicesimplified by direct latent image formation with a charge feed devicecan also be provided.

EXAMPLES 1 TO 9

An improved number of digits in magnitude of electron emission quantitywas checked in a case where an organic compound shown in Table 1 iscaused to be adsorbed on a semiconductor surface of a semiconductorlayer in conditions similar to those of Embodiment 1. Examples 1, 2 and4 correspond to Embodiments 1, 2 and 3, respectively.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 ClassificationAldehyde Aldehyde Aldehyde Unsaturated Unsaturated group group groupbond bond Organic compound n-Decanal n-Dodecanal n-Octanal 1-Decene1-Dodecene Chemical formula CH₃(CH₃)₈ CH₃(CH₂)₁₀ CH₃(CH₂)₆ CH₃(CH₂)₇CH₃(CH₂)₉ CHO CHO CHO CH═CH₂ CH═CH₂ Improved After 5 0.37 1.32 number ofmin. of digits in discharge magnitude After 30 0.82 0.45 2.02 1.25 ofelectron min. of emission discharge current quantity Example 6 Example 7Example 8 Example 9 Classification Unsaturated Two unsaturated Branched& Unsaturated bond bonds unsaturated bond & bond aldehyde group Organiccompound 1-Hexadecene 1,7-Octadiene 2,4-Dymethyl- 2,6-Dymethyl-1-heptene 5-heptenal Chemical formula CH₃(CH₂)₁₃ CH₂═CH(CH₂)₄CH₃(CH₂)₂CH (CH₃)₂C═CH CH═CH₂ CH═CH2 (CH₃)CH₂C (CH₂)₂CH(CH₃) (CH₃)═CH₂CHO Improved After 5 0.53 1.18 0.65 0.46 number of min. of digits indischarge magnitude After 30 of electron min. of emission dischargecurrent quantity

As shown in Table 1, by causing a compound obtained by coupling at leastaldehyde group to a non-cyclic hydrocarbon or a non-cyclic hydrocarbonhaving at least one unsaturated bond to be adsorbed on a semiconductorsurface of a semiconductor layer, an electron emission quantity isincreased by 0.37 to 2.02 digits in magnitude.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

INDUSTRIAL APPLICABILITY

The present invention, as described above, can be widely used in anelectron emitting element and an imaging device using the same.

The invention claimed is:
 1. An electron emitting element of a structurein which a semiconductor layer is formed between an upper electrode anda lower electrode, wherein an organic compound adsorption layer isformed on a semiconductor surface of said semiconductor layer by causinga organic compound to be adsorbed on the semiconductor surface.
 2. Theelectron emitting element according to claim 1, wherein saidsemiconductor layer is made of silicon and a porous siliconsemiconductor layer part or the whole of which is porous.
 3. Theelectron emitting element according to claim 1, wherein saidsemiconductor layer is made of polysilicon and a porous polysiliconsemiconductor layer part or the whole of which is porous.
 4. Theelectron emitting element according to claim 1, wherein said organiccompound is a non-cyclic hydrocarbon.
 5. The electron emitting elementaccording to claim 4, wherein said non-cyclic hydrocarbon is astraight-chain or branched non-cyclic hydrocarbon having 7 or morecarbon atoms in a molecule.
 6. The electron emitting element accordingto claim 4, wherein said non-cyclic hydrocarbon has at least oneunsaturated bond in a molecule.
 7. The electron emitting elementaccording to claim 6, wherein said non-cyclic hydrocarbon having theunsaturated bond is a straight-chain or branched non-cyclic hydrocarbonexpressed by C_(n)H_(2n) (n: an integer ranging from 7 to 17).
 8. Theelectron emitting element according to claim 1, wherein said organiccompound is a compound obtained by coupling at least an aldehyde groupto a non-cyclic hydrocarbon.
 9. The electron emitting element accordingto claim 8, wherein said non-cyclic hydrocarbon is a straight-chain orbranched non-cyclic hydrocarbon having 7 or more carbon atoms in amolecule.
 10. The electron emitting element according to claim 8,wherein said compound obtained by coupling an aldehyde group to anon-cyclic hydrocarbon is a straight-chain or branched saturatedaldehyde compound expressed by C_(n)H_(2n+1)CHO (n: an integer rangingfrom 7 to 17).
 11. The electron emitting element according to claim 8,wherein said compound obtained by coupling an aldehyde group to anon-cyclic hydrocarbon is a straight-chain or branched non-cyclicunsaturated aldehyde compound expressed by C_(n)H_(2n−1)CHO (n: aninteger ranging from 7 to 17).
 12. An imaging device using, as acharger, an electron emitting element of a structure in which asemiconductor layer is formed between an upper electrode and a lowerelectrode, and an organic compound adsorption layer is formed on asemiconductor surface of said semiconductor layer by causing a organiccompound to be adsorbed on the semiconductor surface, wherein anelectrostatic latent image carrier is charged by emitting electrons fromsaid electron emitting element in the atmosphere.
 13. An imaging deviceusing, as a charge feed device, an electron emitting element of astructure in which a semiconductor layer is formed between an upperelectrode and a lower electrode, and an organic compound adsorptionlayer is formed on a semiconductor surface of said semiconductor layerby causing a organic compound to be adsorbed on the semiconductorsurface, wherein a latent image is formed directly on an electrostaticlatent image carrier by emitting electrons from said electron emittingelement in the atmosphere.